Garbage In, Garbage Out (abbreviated to GIGO, coined as a pun on the phrase First-In, First-Out) is a phrase in the field of computer science or information and communication technology. It is used primarily to call attention to the fact that computers will unquestioningly process the most nonsensical of input data (garbage in) and produce nonsensical output (garbage out).
It was most popular in the early days of computing, but applies even more today, when powerful computers can spew out mountains of erroneous information in a short time. The term was coined as a teaching mantra by George Fuechsel, an IBM 305 RAMAC technician/instructor in New York. Early programmers were required to test virtually each program step and cautioned not to expect that the resulting program would "do the right thing" when given imperfect input.
It is also commonly used to describe failures in human decision making due to faulty, incomplete, or imprecise data.
Garbage In, Gospel Out is a more recent expansion of the acronym. It is a sardonic comment on the tendency to put excessive trust in "computerized" data, and on the propensity for individuals to blindly accept what the computer says. Because the data goes through the computer, people tend to believe it.
Decision-makers increasingly face computer-generated information and analyses that could be collected and analyzed in no other way. Precisely for that reason, going behind that output is out of the question, even if one has good cause to be suspicious. In short, the computer analysis becomes the gospel.